Many online mapping systems use tiles to represent portions of a map. A mapping system can use images, such as satellite and aerial images, for the map tiles. The mapping system can also generate the map tiles using vector data that describes geographic features, such as data from a geographic information system (GIS). Typically, rendering a set of map tiles from vector data for a large or complex map can take a significant amount of time, such as days or even weeks.
Once map tiles have been rendered, a client computing device can then download the map tiles from the mapping system and arrange the downloaded map tiles for display in an application window. The map often includes multiple zoom levels, where each map tile in a low, zoomed-in level represents a smaller portion of the map than each tile in a higher, zoomed-out level. In some cases, as a user pans and zooms through the map, the client computing device downloads additional map tiles from the mapping system for display in the application window.